What factors have contributed to climate change in the past and are they contributing to climate change now?
Author
Earth & Space Science
HS-ESS2-4Time: 5 Days
17 Investigative Phenomenon
17.1 🔬 Phenomenon
The amount of radiation received at 65°N has gone up and down over the last 750,000 years and repeats a pattern about every 100,000 years.
17.1.1 Driving Questions:
How do we know that natural cycles aren’t causing climate change today?
How has the Earth’s position with respect to the Sun changed over time?
How does the Earth’s changing position with respect to the Sun affect temperatures on Earth?
18 Engage: Solar Radiation Patterns
18.1 Solar Radiation at 65°N
Connecting to our earlier questions about how Earth’s temperature has varied in the past, let’s analyze the total amount of energy from solar radiation reaching Earth at 65°N over the last 750,000 years.
viewof timeRange = Inputs.range([0,750], {step:50,value:750,label:"View last ___ thousand years:"})
Code
filteredRadData = radiationData.filter(d => d.kya<= timeRange)Plot.plot({title:"Summer Radiation at 65°N Over the Past "+ timeRange +",000 Years",subtitle:"Solar Radiation (Watts/m²)",width:750,height:400,x: {label:"Thousands of Years Ago (kya)",reverse:true},y: {label:"Radiation (W/m²)",domain: [420,550]},marks: [ Plot.ruleY([480], {stroke:"#999",strokeDasharray:"4,4"}), Plot.areaY(filteredRadData, {x:"kya",y:"radiation",y2:480,fill: d => d.radiation>480?"#e74c3c":"#3498db",fillOpacity:0.4}), Plot.line(filteredRadData, {x:"kya",y:"radiation",stroke:"#2c3e50",strokeWidth:2}), Plot.dot(filteredRadData.filter(d => d.radiation>520), {x:"kya",y:"radiation",fill:"red",r:5}), Plot.text(filteredRadData.filter(d => d.radiation>520), {x:"kya",y:"radiation",text: d =>"Peak",dy:-10,fontSize:10}) ]})
18.1.1 ✅ Initial Observations
What pattern do you notice in the radiation data over the last 750,000 years?
Approximately how often does the radiation intensity peak?
How might this repeating pattern relate to the temperature cycles we’ve discussed previously?
19 Explore: Earth’s Orbital Cycles
19.1 The Three Orbital Cycles
How does Earth’s position affect the amount of radiation reaching Earth’s surface? Students use models of Earth’s eccentricity, tilt, and direction of tilt cycles to collect empirical evidence in order to determine whether there is a causal relationship between orbital cycles and the amount of solar radiation reaching Earth at 65° N over the last 750,000 years.
Serbian scientist Milutin Milankovitch proposed that variations in Earth’s orbit cause long-term climate cycles. Let’s explore each one.
19.1.1 Cycle 1: Eccentricity (~100,000 year cycle)
Earth’s orbit changes shape from nearly circular to more elliptical.
Use the interactive simulations above to explore each cycle
Record observations in your data table:
Cycle
Period
Current Value
Range
Climate Effect
Eccentricity
~100,000 yrs
0.017
0.0 - 0.06
Changes total radiation received
Obliquity
~41,000 yrs
23.5°
22.1° - 24.5°
Changes seasonal contrast
Precession
~23,000 yrs
N/A
360° rotation
Changes timing of seasons
Part 2: Analyzing the Data
Review the Radiation Graph from the Engage section.
Which orbital cycle (Eccentricity, Obliquity, or Precession) has a period that most closely matches the major 100,000-year pattern in the radiation data?
How might the other two cycles affect the smaller “wiggles” in the data?
Part 3: Making a Claim
Based on your observations of the orbital models and the radiation data: 1. Construct a claim about whether Earth’s orbital cycles cause the variations in solar radiation reaching Earth. 2. Support your claim with evidence from the models and the graph.
20 Explain: Connecting Orbit to Climate
Did changes in Earth’s position cause the patterns of radiation reaching Earth’s surface and glacial-interglacial cycles?
20.1 🌍 The Mechanism
Key Insight: It’s not total yearly radiation that matters most—it’s summer radiation at high northern latitudes (around 65°N).
20.1.1 Why 65°N Matters:
Most of Earth’s land mass is in the Northern Hemisphere
Ice sheets grow when summer is NOT warm enough to melt winter snow
When summer radiation at 65°N is LOW, ice sheets expand
When summer radiation at 65°N is HIGH, ice sheets retreat
20.1.2 The Feedback Loop:
Low summer radiation → Snow persists → Ice sheets grow →
Higher albedo → More cooling → More ice growth
20.2 Comparing Radiation and Temperature
Code
combinedData = iceCoreTempData.map(d => {const rad = radiationData.find(r => r.kya=== d.kya);return {kya: d.kya,temp: d.temp,radiation: rad ? rad.radiation:480 };})Plot.plot({title:"Temperature vs. Summer Radiation at 65°N",width:750,height:400,x: {label:"Thousands of Years Ago",reverse:true},y: {label:"Temperature Anomaly (°C)",axis:"left"},marks: [ Plot.line(combinedData, {x:"kya",y:"temp",stroke:"#e74c3c",strokeWidth:2}), Plot.dot(combinedData.filter(d => d.temp>-2), {x:"kya",y:"temp",fill:"#e74c3c",r:6}), Plot.text([{x:350,y:2}], {x:"x",y:"y",text: d =>"Temperature",fill:"#e74c3c",fontSize:12}),// Add radiation trend for comparison (scaled to fit) Plot.line(combinedData, {x:"kya",y: d => (d.radiation-480) /10-6,stroke:"#3498db",strokeWidth:1,strokeDasharray:"4,2"}), Plot.text([{x:350,y:-5}], {x:"x",y:"y",text: d =>"Radiation (scaled)",fill:"#3498db",fontSize:10}) ]})
20.2.1 💡 Key Ideas: Earth-Sun Dynamics
Temperatures on Earth have fluctuated greatly during human history, marked by glacial and interglacial periods
A pattern exists in the frequency of these fluctuations (~100,000 years)
The pattern is explained by cyclical changes in Earth’s orbit shape and tilt
These changes cause ice sheets to expand and retreat
Current orbital parameters suggest Earth should be cooling, yet global temperatures are increasing
21 Elaborate: Solar Activity vs. Glacial Cycles
How well does activity from the Sun correlate with glacial-interglacial cycles?
21.1 Solar Radiation Data
Some claim changes in the Sun’s output (Solar Activity) are causing climate changes. We know orbital cycles cause the Ice Ages, but what about the Sun itself? And what about the warming we see today?
Let’s examine the evidence for the Sun’s role in recent history:
Code
solarData = [ {year:1880,tsi:1365.5,temp:-0.16}, {year:1900,tsi:1365.7,temp:-0.08}, {year:1920,tsi:1365.6,temp:-0.25}, {year:1940,tsi:1365.8,temp:0.12}, {year:1960,tsi:1365.9,temp:-0.01}, {year:1980,tsi:1366.1,temp:0.26}, {year:2000,tsi:1366.0,temp:0.42}, {year:2020,tsi:1361.0,temp:1.02}]Plot.plot({title:"Solar Output (TSI) vs Global Temperature",width:700,height:400,x: {label:"Year"},marks: [ Plot.line(solarData, {x:"year",y: d => (d.tsi-1360) *2,stroke:"#f1c40f",strokeWidth:2}), Plot.line(solarData, {x:"year",y: d => d.temp*3+5,stroke:"#e74c3c",strokeWidth:2}), Plot.text([{x:1900,y:12}], {x:"x",y:"y",text: d =>"Solar Output",fill:"#f1c40f",fontSize:12}), Plot.text([{x:1900,y:7}], {x:"x",y:"y",text: d =>"Temperature",fill:"#e74c3c",fontSize:12}) ]})
21.1.1 ✅ Analysis Questions
Has solar output increased significantly since 1980?
Has temperature increased significantly since 1980?
Can changes in solar output explain recent warming? Why or why not?
22 Evaluate: Are Orbital Factors Causing Warming Today?
How do we know that orbital factors are not causing climate change today?
22.1 📊 Putting It Together
Based on current orbital parameters:
Parameter
Current Value
Trend
Climate Effect
Eccentricity
0.017
Decreasing
Less seasonal variation
Obliquity
23.44°
Decreasing
Less extreme seasons
Precession
NH summer at aphelion
Changing slowly
Cooler NH summers
Conclusion: Based on Milankovitch cycles alone, Earth should be gradually cooling. The fact that Earth is warming despite this indicates another factor is at play.
This sets up our next investigation: What IS causing the warming?
22.2 📝 Earth-Sun Dynamics Quiz
Question 1: What is the approximate period of the eccentricity cycle? - A) 23,000 years - B) 41,000 years - C) 100,000 years - D) 1 million years
Question 2: Why is summer radiation at 65°N latitude so important for ice ages? - A) It’s where most people live - B) It’s where most land mass is located, and ice sheets need cool summers to persist - C) The Sun is closest to Earth at this latitude - D) Ocean currents are strongest here
Question 3: Earth’s current axial tilt is approximately: - A) 22.1° - B) 23.5° - C) 24.5° - D) 45°
Question 4: According to Milankovitch cycles, what should Earth’s climate be doing right now? - A) Warming rapidly - B) Staying constant - C) Cooling gradually - D) Experiencing an ice age
Question 5: What causes the ~100,000 year glacial-interglacial cycle? - A) Changes in the Sun’s energy output - B) Volcanic activity - C) Changes in Earth’s orbital eccentricity - D) Human activity
Question 6: The precession cycle affects climate by: - A) Changing total solar radiation received - B) Changing which season occurs at perihelion vs aphelion - C) Changing Earth’s distance from the Sun - D) Changing the Sun’s output
Question 7: If Earth’s axial tilt increased to 24.5°, seasons would become: - A) Less extreme - B) More extreme - C) Unchanged - D) Reversed
Question 8: What is the significance of global warming occurring despite Milankovitch cycles predicting cooling? - A) Milankovitch cycles are wrong - B) Another factor must be causing the warming - C) The Sun’s output has increased dramatically - D) Earth’s orbit has changed unexpectedly